1. Technical Field
The present invention relates to a method of producing electric power with molten carbonate type fuel cell which directry converts chemical energy of fuel to electrical energy, and to an appartatus for carrying out the method.
2. Background Art
A molten carbonate type fuel cell device is well known in the art. This particular fuel cell device is composed of a plurality of fuel cells stacked one after another with separators being inserted between two adjacent fuel cells. Each fuel cell comprises a tile (electrolyte plate) of a porous substance filled with an electrolyte of a molten carbonate, which tile is sandwiched between a cathode electrode (oxygen plate) and an anode electrode (fuel plate), and an oxidizing gas is fed into the cathode electrode while a fuel gas is supplied into the anode electrode so as to cause a reaction between the cathode and the anode and to produce electric power.
In a case where a hydrocarbon or methanol is employed as a fuel in the electric power-producing system using the molten carbonate type fuel cell, first the fuel gas is reformed to a fuel gas and then fed into the anode of the fuel cell.
As the means of reforming the above-mentioned fuel, an external reformation type and an internal reformation type are popular in the art.
As the convetntional external reformation type, one typical system is shown in FIG. 9 of the accompanying drawings, in which a hydrocarbon (natural gas such as methane) that is used as the fuel gas to be fed into the anode b of the fuel cell a is first introduced into the reformer d, and then the hydrogen (H.sub.2) and carbon monoxide (CO) formed therein are introduced into the anode b as the fuel gas and are partially consumed for producing electric power. On the other hand, the anode exhaust gas expelled from the anode b, as containing the non-reacted methane (CH.sub.4), hydrogen (H.sub.2) and carbon monoxide (CO) in addition to the carbon dioxide (CO.sub.2) and water (H.sub.2 O) generated in the fuel cell 1, is supplied into the combustion chamber of the reformer d through a line e and is combusted therein to product a heat necessary for reformation of the fuel gas. The CO.sub.2 -containing gas exhausted from the combustion chamber of the reformer d passes through a line f to be combined with air A and is fed to the cathode c to be utilized for the cell reaction.
On the other hand, one typical system of the conventional internal reformation type is shown in FIG. 10, in which the reformer d is built in the fuel cell a so that the heat from the fuel cell a is directly utilized for the reforming reaction in the reformer d, the anode exhaust gas to be discharged from the anode b is composed of the same components as those constituting the anode exhaust gas in the case of the above-mentioned external reformation type system and contains the non-reacted CH.sub.4, H.sub.2 and CO. The hydrogen (H.sub.2) is separated from the anode exhaust gas in a hydrogen-separator g and is recirculated to the reformer d thorugh a line h via a fuel feed line i to the reformer d while the remaining CH.sub.4, CO and the non-separated H.sub.2 are combusted in a catalyst combusting device i and are fed into the cathode c together with the air A through a line k (U.S. patent Ser. No. 4,532,192).
However, in both these external reformation type and internal reformation type systems, the non-reformed CH.sub.4 contained in the gas exhausted from the anode b and CO and H.sub.2 not reacted in the fuel cell are combusted and then fed into the cathode c together with the air. Therefore, these systems have a drawback that the CH.sub.4, CO and H.sub.2 can not be completely utilized in the cell reaction but are combusted to be converted into a heat energy. Hence, the power-producing efficiencty is poor. In addition, the methane (CH.sub.4) which is not reformed in the reformer d would cause a deterioration of the power-producing efficiency. Such a deterioration has to be counterbalanced by a certain measure. For this purpose, generally an amount of the steam for reformation is increased and the reaction temperature for reformation is elevated. Still another problem is that the H.sub.2 and CO not used in the fuel cell would also cause a depression of the power-producing efficiency. If the utilization factor of these gases is raised, the cell potential would drop, and therefore, a part of these H2, and CO are inevitable to remain as they are not used. Moreover, there is still another problem that the non-combusted gas from the fuel cell contains carbon dioxide gas which is a low caloric gas. Therefore, an expensive catalyst combustion device is necessary for combusting the gases.